Vacuum processing apparatus

ABSTRACT

The invention provides a plasma processing apparatus for processing a wafer mounted on a sample stage placed in a vacuum processing chamber using a plasma generated in the vacuum chamber. The plasma processing apparatus comprises a plate placed in the vacuum processing vessel above and opposed to the wafer, the plate having a through hole through which a first processing gas is introduced; a first and second cylindrical member arranged vertically and adjacently; and means communicating with the gap between the first and second cylindrical member for supplying a second processing gas. The wafer is processed while the first processing gas and the second processing gas having different compositions are supplied.

The present application is a continuation of U.S. patent applicationSer. No. 11/683,040, filed Mar. 7, 2007, and is based on and claimspriority of Japanese Patent application No. 2006-305138 filed on Nov.10, 2006, the entire contents of which are hereby incorporated byreference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to a vacuum processing apparatus for processingsemiconductor wafers or other substrate samples in a decompressedprocessing chamber in a vacuum vessel while a processing gas isintroduced into the processing chamber.

2. Description of the Related Art

Conventionally, in a vacuum processing apparatus for processingsemiconductor wafers or other substrate samples to manufacturesemiconductor devices, a processing chamber is placed in a vacuum vesseland decompressed to a predetermined degree of vacuum, and a processinggas is introduced into the processing chamber to form a desired featureon the semiconductor wafer surface. For example, an electric field issupplied from outside the vacuum vessel to a reactive gas introducedinto the processing chamber to turn it into a plasma. By physical andchemical reactions with reactive particles such as ions and othercharged particles and radicals in the plasma, a thin film previouslyformed on the wafer surface is processed into a desired feature.

The demand for higher integration of semiconductor devices requires sucha vacuum processing apparatus to process a substrate surface with higherdefinition and accuracy. To meet such requirement, the sample surfacemust be processed more uniformly. For example, if the processing resultsignificantly varies at different sites on the sample surface, asemiconductor device processed with a larger deviation from the desiredfeature fails to reach expected performance as compared with otherdevices, and the device manufacturing yield may decrease.

In view of this, for uniform processing, the processing gas introducedinto the processing chamber is required to have a more uniform densitydistribution in the processing chamber. That is, it is known that suchgas distribution greatly affects the uniformity of processingperformance. Thus, conventionally, the introduction of gas is designedso that the gas distribution is uniform on the semiconductor wafersurface. For example, the processing chamber is shaped like a cylinder,the sample stage placed in the processing chamber for mounting asemiconductor wafer thereon has a generally cylindrical shape, and theyare arranged coaxially or concentrically. Thus the processingperformance is made uniform in the circumferential direction of adisc-shaped semiconductor wafer sample.

However, the temperature of a semiconductor wafer during processing andreaction products generated in processing the semiconductor wafer haveradially nonuniform distribution. Recently, there is a demand for takingthis into consideration to realize more uniform processing within thesemiconductor wafer surface. For example, in a technique for enhancingthe uniformity of processing performance, the component ratio ofmaterials constituting a processing gas is varied radially with respectto the semiconductor wafer, and such a processing gas is supplied intothe processing chamber above the semiconductor wafer so that eachcomponent has a different distribution above the semiconductor wafer.

An example conventional technique like this is disclosed in JP62-290885A. In this conventional technique, cells are placed at theupside of the processing chamber and opposed to the semiconductor wafer.Processing gases of different species and flow rates are supplied to theelectrode in the cells. A plurality of introduction holes forintroducing the processing gases into the processing chamber areprovided in communication with the cells, respectively. Gases ofdifferent gas species and gas flow rates are introduced from the gasintroduction holes.

According to the configuration of such conventional technique,processing gases are introduced from a plurality of locations includingthe vicinity of the central axis and the vicinity of the outer peripheryof the processing chamber into a space for plasma excitation anddiffusion of the processing gases above the sample stage for mounting awafer. Processing gases of different gas species and gas flow rates areintroduced from these introduction locations to obtain a differentconcentration distribution for each gas species on the wafer surface.

In such conventional technique, in a processing chamber having a largespace between the locations for introducing processing gases and thesample stage, the gas concentration distribution is flattened due to gasdiffusion even if processing gases of different gas species and gas flowrates are introduced from different locations including the vicinity ofthe central axis and the vicinity of the outer periphery. Hence it isdifficult to produce a biased distribution of gas concentration on thewafer surface. To overcome this difficulty, the variation of gasconcentration distribution on the wafer surface can be increased byintroducing processing gases from positions nearer to the wafer, e.g.,from the side face of the processing chamber beside the above-mentionedspace or from the surface on the outer periphery side of the samplestage (JP 10-064881A)

However, in the above conventional techniques, the following point isnot sufficiently taken into consideration. In the conventional techniquewhere gas is introduced from the vicinity of the wafer position toincrease the variation of gas concentration distribution on thesemiconductor wafer surface, introduction holes for introducing theprocessing gas must be provided on the inner surface of the processingchamber such as the side face of the processing chamber or the outersurface of the sample stage. Depending on the shape of the introducinghole, the distribution of the processing gas component in the processingchamber may be significantly deviated from the axisymmetricaldistribution. Thus, unfortunately, the axisymmetrical plasma density inthe processing chamber cannot be achieved, and the processing uniformityis significantly impaired.

SUMMARY OF THE INVENTION

An object of the invention is to provide a vacuum processing apparatuscapable of uniformly processing a sample placed on the sample stage inthe processing chamber.

The above object is achieved by a plasma processing apparatus forprocessing a wafer mounted on a sample stage placed in a vacuumprocessing chamber using a plasma generated in the vacuum chamber, theplasma processing apparatus comprising: a plate placed in the vacuumprocessing vessel above and opposed to the wafer, the plate having athrough hole through which a first processing gas is introduced; a gapspace having a generally cylindrical shape formed in the processingchamber; and means communicating with the gap for supplying a secondprocessing gas, wherein the wafer is processed while the firstprocessing gas and the second processing gas having differentcompositions are supplied.

According to the invention, it is advantageously possible to provide avacuum processing apparatus capable of uniformly processing asemiconductor wafer so that gas supply in the space above the sample ismade more uniform in the circumferential direction of the sample.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 schematically shows the overall configuration of a vacuumprocessing apparatus according to a first embodiment of the invention.

FIG. 2 is a vertical cross-sectional view schematically showing theconfiguration of the processing unit of the embodiment shown in FIG. 1.

FIG. 3 is a vertical cross-sectional view schematically showing theconfiguration around the gas diffusion ring of the processing unit shownin FIG. 2.

FIG. 4 is a perspective view schematically showing the configuration ofthe vacuum vessel and the gas diffusion ring.

FIG. 5 is a perspective view schematically showing the configuration ofthe gas diffusion ring shown in FIG. 3.

FIG. 6 is a vertical cross-sectional view schematically showing theconfiguration of the main part of a processing unit according to avariation of the first embodiment shown in FIG. 1.

FIG. 7 is a vertical cross-sectional view schematically showing theconfiguration of the main part of a processing unit according to anothervariation of the first embodiment shown in FIG. 1.

FIG. 8 is a vertical cross-sectional view schematically showing theconfiguration of the main part of a processing unit according to asecond embodiment of the invention.

FIG. 9 is a vertical cross-sectional view schematically illustrating theconfiguration of the main part of a processing unit according to anothervariation of the first embodiment shown in FIG. 1.

FIG. 10 is a vertical cross-sectional view schematically showing theconfiguration of the main part of a processing unit according to anothervariation of the first embodiment shown in FIG. 1.

FIG. 11 is an enlarged vertical cross-sectional view showing theconfiguration in the vicinity of the gas diffusion ring of theprocessing unit according to the variation shown in FIG. 10.

FIG. 12 is a vertical cross-sectional view schematically showing theconfiguration of the main part of a processing unit according to a thirdembodiment of the invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Embodiments of the vacuum processing apparatus according to theinvention will now be described with reference to the drawings.

First Embodiment

A first embodiment of the invention is described with reference to FIGS.1 to 5. FIG. 1 schematically shows the overall configuration of a vacuumprocessing apparatus according to the first embodiment of the invention.FIG. 1A is a horizontal cross-sectional view schematically showing theconfiguration of the vacuum processing apparatus as viewed from above.FIG. 1B is a perspective view of the vacuum processing apparatus.

The vacuum processing apparatus 100 according to this embodiment shownin FIG. 1 is generally divided into an atmosphere side block 101 and avacuum side block 102. In the atmosphere side block 101, a wafer istransferred, stored, or positioned under atmospheric pressure. In thevacuum side block 102, a wafer or other substrate sample is transferredand processed in a predetermined processing unit under a pressurereduced below atmospheric pressure. Between the location for thesetransferring and processing operations and the atmosphere side block101, the vacuum processing apparatus 100 has a section for varying thepressure from atmospheric pressure to vacuum pressure or vice versa witha sample placed therein.

The atmosphere side block 101 includes a housing 106 having a generallyrectangular solid shape equipped therein with an atmospheric transferrobot 109. The atmosphere side block 101 further includes a plurality ofcassette stages 107 attached to the frontside (right side in the figure)of the housing 106. A cassette containing samples to be processed or tobe cleaned can be mounted on the cassette stage 107.

The vacuum side block 102 includes a vacuum transfer vessel 104 having agenerally polygonal (pentagonal in this embodiment) planar shape. Aroundthe sidewall of the vacuum transfer vessel 104, the vacuum side block102 includes four processing units 103 and two lock chambers 105. Theprocessing unit 103 is equipped with a vacuum vessel having a processingchamber, in which a sample is transferred and processed under reducedpressure. The lock chamber 105 is placed between the vacuum transfervessel 104 and the atmosphere side block 101, and exchanges a samplebetween the atmosphere side and the vacuum side. The vacuum side block102 can be maintained at a reduced pressure of a high degree of vacuum.

The vacuum transfer vessel 104 includes a transfer chamber. A vacuumtransfer robot 108 for transferring a sample between a lock chamber 105and the processing chamber in a processing unit 103 under vacuum isplaced at the center of the transfer chamber. A sample is mounted on thearm of the vacuum transfer robot 108 and transferred between a samplestage placed in the processing chamber of each processing unit 103 and asample stage in any one of the lock chambers 105. Each of the processingunits 103 and the lock chambers 105 communicates with the transferchamber in the vacuum transfer vessel 104 through a channel that can behermetically opened and closed by a valve.

Processing of a plurality of semiconductor wafers or other samplescontained in a cassette mounted on one of the cassette stages 107 isstarted upon determination of a controller, not shown, that controls theoperation of the vacuum processing apparatus 100, or upon receipt of acommand from a controller of the manufacturing line on which the vacuumprocessing apparatus 100 is installed. Upon receipt of a command fromthe controller, the atmospheric transfer robot 109 retrieves a specificsample from the cassette, and transfers it to one of the two lockchambers.

The lock chamber 105 is sealed by closing the valve with the transferredsample being contained, and is decompressed to a predetermined pressure.Then, by opening the valve on the side facing the transfer chamber inthe vacuum transfer vessel 104, the lock chamber 105 gets incommunication with the transfer chamber. The arm of the vacuum transferrobot 108 stretches into the lock chamber 105, and transfers out thesample therein. The sample mounted on the arm of the vacuum transferrobot 108 is transferred into the evacuated processing chamber in one ofthe processing units 103, which is predetermined when the sample istransferred from the cassette.

After the sample is transferred into the processing chamber in one ofthe processing units 103, the valve between this processing chamber andthe transfer chamber is closed to seal the processing chamber. Then aprocessing gas is introduced into the processing chamber, a plasma isgenerated in the processing chamber, and the sample is processed.

When completion of processing of the sample is detected, theabove-mentioned valve is opened, and the sample is transferred out bythe vacuum transfer robot 108 toward the lock chamber 105 in a reversemanner to its transfer into the processing chamber. After the sample istransferred into one of the lock chambers 105, the valve for opening andclosing the channel between this lock chamber 105 and the transferchamber is closed to seal the interior, and the pressure in the lockchamber 105 is raised to atmospheric pressure.

Then the valve on the housing 106 side is opened to allow the lockchamber 105 to communicate with the atmospheric transfer chamber in thehousing 106. The sample is transferred from the lock chamber 105 to theoriginal cassette and returned to the original position therein by theatmospheric transfer robot 109.

FIG. 2 is a vertical cross-sectional view schematically showing theconfiguration of the processing unit of the embodiment shown in FIG. 1.In particular, among the processing units 103 in FIG. 1, FIG. 2 showsthe configuration of one of the processing units 103 placed behind(upper-left side in FIG. 1) the vacuum transfer vessel 104. In thisembodiment, these two processing units 103 are etching units for etchinga film on the surface of the sample using a plasma.

In this figure, the processing unit 103 includes a vacuum vessel, aradio wave source placed at the upside thereof, and an exhaust apparatusplaced below the vacuum vessel. The vacuum vessel has a lid 201 placedon top, a gas introduction ring 202, a gas diffusion ring 204, and avacuum vessel wall member 205 having a generally cylindrical shape. Theyare each hermetically connected by sealing means such as O-rings, notshown, so that the gas pressure difference between the interior spaceand the exterior space can be maintained at a high level.

The vacuum vessel wall member 205 includes therein a processing chamber217 having a generally cylindrical shape, which is formed by the innerwall of the vacuum vessel wall member 205. In the processing chamber217, a sample stage 208 having a generally cylindrical shape is placedgenerally concentrically with the center of the processing chamber 217.A substrate sample W to be processed can be mounted on the upper surfaceof the sample stage 208.

From an opening of the vacuum vessel wall member 205 placed directlybelow the sample stage 208 at the bottom of the processing chamber 217,the space inside the processing chamber 217 is exhausted by a vacuumpump 209 and maintained at a high degree of vacuum (the arrow in thefigure). The vacuum pump 209 is an exhaust apparatus connected to thebottom of the vacuum vessel wall 205. In particular, in this embodiment,the opening at the bottom of the vacuum vessel wall member 205, whichserves as the inlet of the vacuum pump 209, is arranged generallyconcentrically with the sample stage 217. Gas and particles includingproducts associated with the processing in the processing chamber 217pass around the outer periphery of the sample stage 208 and through thespace below the sample stage 208, and are exhausted concentrically withrespect to the processing chamber 217.

As the processing gas for processing the sample, a gas containing asingle material or a mixed gas containing a plurality of materials at apredetermined ratio and an optimal flow rate ratio is used for eachprocessing condition. In this embodiment, as the processing gas used foretching, a first mixed gas and a second mixed gas having different gasspecies or gas flow rates can be simultaneously introduced into thespace above the sample stage 208 in the processing chamber 217. Asdescribed later, the first mixed gas is provided at a positionconstituting the ceiling of the processing chamber 217 and opposed tothe sample W mounted on the sample stage 208. The first mixed gas isintroduced into the processing chamber 217 from a gas diffusion plate206 having a plurality of through holes 207 for introducing gas. Thethrough holes 207 are located in the vicinity of the center of theprocessing chamber 217.

The first mixed gas is introduced into the space between the lid 201 andthe gas diffusion plate 206 from the gas introduction ring 202, which isplaced above the sidewall upper end of the vacuum vessel wall member 205and constitutes the vacuum vessel. The first mixed gas fills this spaceand enters the vacuum processing chamber through the plurality ofthrough holes 207 below the space. The gas diffusion plate 206 is madeof a generally circular plate placed generally concentrically with thesample stage 208, and the outer edge of the gas diffusion plate 206 issupported. The through holes 207 are located in a concentric region witha diameter slightly smaller than that of the sample W. The processinggas that has entered the processing chamber 217 from the through holes207 diffuses and spreads in the space inside the processing chamber 217.The introduction of the processing gas is regulated so that theprocessing gas has an approximately uniform distribution on the surfaceof the sample W.

The second mixed gas is introduced into the processing chamber 217 froma gas diffusion ring 204 placed above the upper end of the vacuum vesselwall member 205. The second mixed gas introduced from the gas diffusionring 204 passes through a gap with a ring cover 203 and is introducedinto the downside of the processing chamber 217 so as to travel fromabove the sample W on the outer periphery side of the sample stage 208toward the sample W. The ring cover 203 covers the front of the gasdiffusion ring 204 and constitutes the inner wall of the processingchamber 217. The introduced second mixed gas diffuses in the spaceinside the processing chamber 217 with a distribution of concentrationthat is high on and toward the outer periphery of the sample W and lowat the wafer center.

The processing gas containing the first mixed gas and the second mixedgas thus introduced into the processing chamber 217 interacts with anelectric and magnetic field from the radio wave source placed at theupside of the vacuum vessel and the magnetic field source placed aroundthe vacuum vessel. Atoms and molecules in the gas are excited byelectron cyclotron resonance and turned into a plasma. The radio wavesource includes a magnetron 211 placed above the gas introduction ring202 on top of the vacuum vessel and the lid 201 with its outer edgebeing mounted and held on the gas introduction ring 202. The radio wavesource further includes a waveguide 215 for introducing radio waves fromthe magnetron 211 through the lid 201 into the processing chamber 217.Furthermore, a solenoid coil 212 for supplying a magnetic field into theprocessing chamber 217 is placed around the lid 201 or the vacuum vesselwall member 205.

The sample stage 208 includes therein an electrode made of conductor, towhich a high-frequency bias power supply 213 is connected.High-frequency power applied by the high-frequency bias power supplyproduces a bias potential on the surface of the sample W, and chargedparticles in the plasma are attracted by the bias potential and collidewith the surface of the sample W, thereby causing a physical reaction.On the other hand, radicals chemically react with the wafer surface.Synergy of these physical and chemical reactions advances etching of thesurface of the sample W.

When a semiconductor wafer is etched as the sample W, the concentrationof reaction products containing silicon is lower in the region on theouter periphery side of the sample W than in the center side, and thetemperature differs between the outer periphery side and the center sideof the surface of the sample W. Hence radial nonuniformity may occur inthe processing of the sample W. In this embodiment, the gas species andgas flow rates of the first mixed gas and the second mixed gas areindependently regulated to control the gas concentration distribution onthe wafer surface. Thus the radial nonuniformity in processingperformance due to the above factors is canceled to provide a uniformprocessing performance in the wafer radial direction.

More specifically, the first mixed gas is introduced from a ductcommunicating with a gas supply pipe coupled to the gas introductionring 202. The second mixed gas is introduced from another ductcommunicating with a gas supply pipe coupled to the gas diffusion ring204. Opening/closing valves 216, 216′ are provided on these ducts andregulate the introduction of the first and second mixed gas into theprocessing chamber 217, respectively. A plurality of supply pipes forsupplying material gases are connected to each of the ducts. The flowrates of these material gases are regulated by flow rate regulators 210a, 210 b, 210 c, 210 d, and the gases are supplied to each duct.

Next, the configuration for introducing the second mixed gas into theprocessing chamber 217 is described in detail with reference to FIG. 3,which is a vertical cross-sectional view schematically showing theconfiguration around the gas diffusion ring of the processing unit shownin FIG. 2.

In this figure, the gas diffusion ring 204 is mounted on the upper endof the grounded vacuum vessel wall member 205. The gas diffusion ring204 is held by being sandwiched on its upper and lower face between thevacuum vessel wall member 205 and the ring cover 203 mounted on the gasdiffusion ring 204. The gas diffusion ring 209 is a ring-shaped memberhaving a rectangular cross section, and includes therein a gas channel301, which is a ring-shaped communicating space. The outer peripheralsidewall of the gas diffusion ring 204 is exposed outside the vacuumvessel to constitute the vacuum vessel outer wall, to which a gas supplypipe 304 for introducing the second mixed gas into the gas channel 301is coupled. On the other hand, gas introduction holes 302 are located onthe inner peripheral sidewall of the gas diffusion ring 204 beingdisposed at almost the entire circumference of the processing chamber217 or the sample stage 208 and communicate with the gas channel 301therein. Gas flows out of the gas introduction hole 302 toward the innerperiphery. The gas introduction hole 302 may be a slit formed along thecircumferential direction and having a predetermined width. The secondmixed gas passes through the gas channel 301 and a plurality of gasintroduction holes 302, which penetrates the gas ring 204, and isintroduced inward through the sidewall at the upside of the processingchamber 217 at a circumferentially predetermined flow rate.

The ring cover 203 is located above and inside the gas diffusion ring204, and covers the gas introduction hole 302 at the inner peripheralsidewall of the gas diffusion ring 204. The ring cover 203 includes aflange sandwiched between the upper face of the gas diffusion ring 204and the lower face of the gas introduction ring 202. The ring cover 203further includes an extending portion continued from the flange andconstituting the upper inner wall of the processing chamber 217. Theextending portion extends downward so as to cover the inner wall of thegas diffusion ring 204 and the upper end of the vacuum vessel wallmember 205.

The ring cover 203 is attached to the vacuum vessel with a gap 303 of agenerally uniform width in the circumferential direction of the gasdiffusion ring, where the surface of the extending portion facing towardthe outside of the processing chamber 217 is opposed across the gap 303to the inner peripheral wall of the gas diffusion ring 204 and the innerwall of the upper end of the vacuum vessel wall 205. According to thisconfiguration, a gap 303′ is formed between the inner peripheral wall ofthe gas diffusion ring 204 and the outer side face of the ring cover203. The gap 303′ further communicates with the opening 303″ of the gap303 located generally circumferentially on the inner wall of theprocessing chamber 217 above the sample stage 208. The second mixed gasintroduced from the gas introduction hole 302 of the gas diffusion ring204 into the gap 303′ passes through the gap 303 between the extendingportion of the ring cover 203 and the upper end of the vacuum vesselwall 205, passes through the opening 303″ located at the lower end ofthe ring cover 203, and is introduced into the space in the processingchamber 217 where a plasma is generated.

The gap 303 in this embodiment is directed toward the center (inward) ofthe processing chamber 217 as it goes downward from the upper gap 303′facing toward the inner peripheral wall of the gas diffusion ring 204.Thus the lower portion of the ring cover 203 has a tapered shape whereits outer peripheral surface is sloped toward the inside of theprocessing chamber 217. That is, the lower end is shaped so that itsthickness in the inside-outside direction decreases downward.Furthermore, the portion of the vacuum vessel wall member 205 facing theouter peripheral surface of this lower end and constituting the gap forintroducing gas has a tapered shape sloped outward, and its thickness inthe inside-outside direction decreases upward.

The ring cover 203 and the vacuum vessel wall member 205 are located soas to face a plasma generated in the processing chamber 217. The gasdiffusion ring 204 is covered therewith so as not to directly face theplasma. In this embodiment, the ring cover 203 and the vacuum vesselwall member 205 are illustratively made of an aluminum alloy basematerial covered with alumite (Al₂O₃) or other material having highplasma resistance. The gas diffusion ring 204, which is not directlyexposed to plasma but allows the processing gas to flow therethrough, isillustratively made of stainless steel or other material having goodcorrosion resistance.

Like the vacuum vessel wall member 205, the ring cover 203 is shaped sothat its inner wall exposed to plasma is concentric with the processingchamber 217. The ring cover 203 is located generally coaxial with thecentral axis of the sample stage 208. The gaps 303 are uniformly spacedgenerally circumferentially around the center of the sample W. Thus theeffect of the gas introduced from the gaps 303 on the plasma processingof the surface of the sample W reduces circumferential nonuniformity,and enhances the circumferential uniformity of processing performance.

In this embodiment, a plurality of gas introduction holes 302 areprovided in the gas diffusion ring 204 generally symmetrically withrespect to the center of the sample stage 208 and discretely in thecircumferential direction. Thus the axisymmetry is broken at theposition of the gas introduction hole 302. However, the gas diffusionring 204 is placed at a position not directly facing the plasma toprevent the gas introduction hole 302 from adversely affecting thesymmetry of processing on the surface of the sample W.

More specifically, when the second mixed gas is introduced from the gassupply pipe 304 into the gas channel 301 communicating therewith andlocated inside the gas diffusion ring 204, the gas fills the gas channel301, which is a space connected in a ring shape. At this time, part ofthe second mixed gas in the gas channel 301 starts to flow from the gasintroduction hole 302 into the gap 303′.

However, in this embodiment, the shape including the diameter and heightof the gas introduction hole 302 is small enough to prevent the secondmixed gas from easily flowing therethrough, and hence the flow channelhas a large resistance (or small conductance). Thus most of the secondmixed gas fills the ring-shaped gas channel 301 at a predeterminedpressure.

Thus the second mixed gas in the gas channel 301 reaches a predeterminedpressure. Then the second mixed gas passes through the gas introductionhole 302 and flows into the gap 303′ at a flow rate determined by thebalance between the pressure difference relative to the interior of thegap 303′ and the resistance in the flow channel of the gas introductionhole 302. Here, as described above, the gas introduction holes 302 areuniformly spaced along the inner periphery of the gas diffusion ring204, and the gas channel 301 is filled with the second mixed gas. Thus,between the gas introduction holes 302, the difference in the amount ofthe second mixed gas supplied therethrough to the gap 303′ is reduced.

However, in order to sufficiently reduce the difference in the amount offlow rate in a plurality of gas introduction holes 302, the diameter orheight thereof must be significantly reduced, and working for realizingsuch configuration increases cost. Furthermore, unfortunately, in somecases, deformation occurs in the shape of the gas diffusion ring 204subjected to such working, and makes it difficult to use the gasdiffusion ring 204 as part of the vacuum vessel and maintain hermeticsealing thereof.

On the other hand, when the gas introduction hole 302 is shaped so as toreduce working cost and deformation, a large difference occurs in theflow rate between the plurality of gas introduction holes 302. In thiscase, if the second mixed gas is introduced into the processing chamber217, nonuniformity occurs in the gas density and the distribution ofplasma and reaction products on the sample W particularly in thecircumferential direction. To solve this, in this embodiment, asdescribed above, a ring cover 203 is placed inside the gas diffusionring 204, and through the gap 303 therebetween, the processing gas isintroduced into the processing chamber 217. This embodiment isconfigured so that the size of the gap 303 is larger than the diameteror height of the gas introduction hole 302.

The second mixed gas is introduced from the high-pressure gas channel301 into the low-pressure gap 303′ and flows from the gap 303′ downwardinto the gap 303. The second mixed gas further diffuses while flowingthrough the decompressed gap 303. Then the second mixed gas flows intothe processing chamber 217 from a gas introduction slit 303″, which isan outlet of the gap 303 on the inner wall of the processing chamber217. Thus the gas introduced from the gas introduction hole 302 into thegap 303′ is provided with a sufficiently uniform flow rate and suppliedto the processing chamber 217. Hence the second mixed gas flowing inwardfrom the upper sidewall of the processing chamber 217 has a more uniformflow rate in the circumferential direction.

FIG. 4 is a perspective view schematically showing the configuration ofthe vacuum vessel and the gas diffusion ring. As shown, in thisembodiment, the ring cover 203, the gas diffusion ring 204, and thevacuum vessel wall member 205 are vertically stacked with the upper andlower face abutting each other.

Among them, the ring cover 203 and the gas diffusion ring 204 areconfigured to be detachable from the vacuum vessel for replacement byopening the vacuum vessel to atmosphere. The grounded ring cover 203constitutes the upper inner wall of the processing chamber 217 and facesthe plasma. Hence reactants generated in the plasma or products derivedfrom the surface of the sample W fly and attach to the ring cover 203,or the ring cover 203 is ablated by collision with charged particles inthe plasma. Thus, repeated processing increases an adverse effect on theprocessing of the sample W and requires the ring cover 203 to bereplaced. With regard to the gas diffusion ring 204, although coveredwith coating having high corrosion resistance, the coating peels off orsuffers from corrosion. Then the gas diffusion ring 204 needs replacing.In this case, the vacuum vessel is opened to atmosphere, and the lid201, the gas introduction ring 202, and the gas diffusion plate 206 aredetached. Then the ring cover 203 and the gas diffusion ring 204 aredetached in this order, and replacement parts are attached in thereverse order.

FIG. 5 is a perspective view schematically showing the configuration ofthe gas diffusion ring shown in FIG. 3. FIG. 5A shows an example wherethe gas introduction hole 302 of the gas diffusion ring 204 is composedof a plurality of through holes. FIG. 5B shows an example where the gasintroduction hole 302 of the gas diffusion ring 204 is composed of oneor more slits arranged circumferentially.

In these figures, the gas diffusion ring 204 is a vertical combinationof a plurality of (two) members, which are hermetically connected toeach other to form an inner space as a gas channel 301. In FIG. 5A, aring-shaped upper member 501 is connected to a ring-shaped lower member502 having a rectangular U-shaped vertical cross-section at its upperface of the walls on the inner periphery side and the outer peripheryside thereof.

The lower member 502 is a ring-shaped member having a recess 505 betweenthe inner peripheral wall and the outer peripheral wall. The recess 505is combined with the upper member 501 to constitute a gas channel 301.As described above, the end of a gas supply pipe 304 is coupled to theouter wall. In the inner wall, a plurality of through holes 503communicating with the recess 505 are uniformly spaced in thecircumferential direction of the ring and at an generally equal heightfrom the upper end or lower end. The through holes 503 serve as the gasintroduction hole 302 when the upper member 501 is combined with thelower member 502.

As described above, the diameter of the through hole 503 is sufficientlysmaller than the width or depth of the recess 505. Thus, when the secondmixed gas is introduced, the gas channel 301 is entirely filled withthis gas, thereby reducing the difference in flow rate of the gasflowing from the plurality of gas introduction holes 302. Although notshown, on the upper end of the walls of the lower member 502 on theinner periphery side and the outer periphery side, O-rings or othersealing members having high corrosion resistance are placed inconformity with the ring shape of the upper ends for sealingtherebetween.

FIG. 5B shows, as in FIG. 5A, a configuration where an upper member 506is mounted on and connected to a member 507 having a recess 505 thereinand coupled to a gas supply pipe 304. In contrast to the example of FIG.5A, a plurality of projections 508 are located circumferentially on theupper end face of the inner wall of the lower member 507, and the upperface of the projections 508 abuts the upper member 506 to form slits 509between the lower member 507 and the upper member 506. The upper endface of the inner wall of the lower member 507 has a generally equalheight from the lower end of the lower member 507, and a plurality ofprojections 508 are equally spaced in the circumferential direction.

The lower member 507 is connected to the upper member 506 at the upperend face on the outer periphery side. As in FIG. 5A, a sealing member isplaced on this upper end face. With the upper member 506 being connectedto the lower member 507, the recess 505 serves as a gas channel 301. Thesecond mixed gas introduced from the gas supply pipe 304 fills the gaschannel 301 and flows out of the slits 509 serving as the gasintroduction hole 302 throughout the inner periphery of the gasdiffusion ring 204.

The gas diffusion ring 204 of this embodiment can be made of an aluminumalloy covered with a material having high corrosion resistance. In viewof not directly facing the processing chamber 217, the gas diffusionring 204 can be made of SUS having high corrosion resistance. Inparticular, the mating surface of the upper and lower member, whichforms slits of the gas supply hole 302, needs corrosion-resistantcoating.

First Variation

Variations in the embodiment of the invention are described withreference to FIGS. 6 and 7. FIG. 6 is a vertical cross-sectional viewschematically showing the configuration of the main part of a processingunit according to a variation of the embodiment shown in FIG. 1. Thesame elements as those in the embodiment of FIGS. 1 to 5 may be referredto by their reference numerals, but are not described in detail.

In the first embodiment, on the inner wall of the processing chamber217, the second mixed gas is introduced downward from above the sample Wtoward the inside. However, as shown in this figure, this variation isdifferent from the first embodiment in that, on the inner wall of theprocessing chamber 217, the second mixed gas is introduced upward towardthe inside. In particular, the gas diffusion ring 204 is located lowerthan the sample W. Gas flows upward from this gas diffusion ring 204toward the inside of the processing chamber 217.

In this variation, the vacuum vessel wall member 205 is composed of anupper wall member 601 and a lower wall member 602 arranged vertically,and a gas diffusion ring 204 is sandwiched and held therebetween. Theouter peripheral wall of the gas diffusion ring 204 is exposed toatmosphere outside the vacuum vessel and constitutes the outer wall, andthe inner peripheral wall is opposed to the lower wall member 602 acrossa gap 603.

The gap 603 is composed of a space between the inner peripheral wall ofthe gas diffusion ring 204 and the lower wall member 602, as well as aspace thereabove between the upper wall member 601 and the lower wallmember. Thus, from the inside of the gas diffusion ring, the gap 603extends upward to the inner wall of the processing chamber 217. Theopening of the gap 603 facing the processing chamber 217 is located witha generally uniform width in the circumferential direction above thesample stage 208. Thus the amount of the second mixed gas flowing fromthe gas diffusion ring 204 into the processing chamber 217 has a reducedcircumferential variation on the outer periphery side of the sample W.

The upper end of the lower wall member 602 constitutes the inner wall ofthe processing chamber 217, where the portion constituting the gap 603has a tapered shape sloped toward the inside as it goes upward. That is,the thickness of the lower wall member 602 in the inside-outsidedirection decreases upward, whereas the thickness of the upper wallmember 601 opposed across the gap increases upward. Also in thisvariation, the second mixed gas introduced into the gas diffusion ring204 flows along the inner sidewall through the gap 903 and diffuses intothe processing chamber 217. Thus the amount of gas introduced into theprocessing chamber 217 from the outer periphery side of the sample W hasan enhanced uniformity, which enhances the uniformity of processing onthe sample W.

Second Variation

FIG. 7 is a vertical cross-sectional view schematically showing theconfiguration of the main part of a processing unit according to anothervariation of the embodiment shown in FIG. 1. This variation is differentfrom the first embodiment in that the gap 303 formed from the ring cover203 and the vacuum vessel wall member 205 protrudes toward the samplestage 208′. The same elements as those in the embodiment of FIGS. 1 to 5may be referred to by their reference numerals, but are not described indetail.

In FIG. 7, the processing chamber 217 of this variation has a concentricconfiguration as in the first embodiment. However, the discharge spaceabove the sample stage 208′, in which a plasma is generated, isdifferent in diameter from the space therebelow, where the lower spacehas a larger diameter. More specifically, the upper portion of thevacuum vessel wall member 205 protrudes toward the center of theprocessing chamber 217 to form a protrusion 701 having a largerthickness, and a ring cover 203 covers the protrusion 701 on theprocessing chamber 217 side. Furthermore, the opening 303″ at the lowerend of the gap 303 formed from the protrusion 701 and the ring cover 203is located near a space 702 on the outer periphery side of the samplestage 208′ below the discharge space where the diameter of theprocessing chamber 217 increases.

This variation allows gas and particles in the processing chamber 217 toflow more easily from the enlarged space 702 toward the space below thesample stage 208′, thereby enhancing the exhaust efficiency.Furthermore, the second mixed gas introduced from the gap 303″ into theprocessing chamber 217 extends at a position protruding toward thesample W on the sample stage 208′, thereby further enhancing theuniformity of processing as well as locally affecting the processing ofthe outer periphery of the surface of the sample W. In this variation,the inner wall of the processing chamber 217 has a step. However, theinner wall of the processing chamber 217 may be gradually divergeddownward (having a trapezoidal vertical cross section).

For example, the sample W is mounted on a projection constituting themounting surface above the sample stage 208′. On the other hand, thesample stage 208′ includes therein a temperature controller such as arefrigerant channel or heater placed concentrically or helically withrespect to the center, which adjusts the temperature of the sample W toa desired distribution during processing. However, temperatureadjustment by the above-mentioned temperature controller is difficult onthe outer edge of the sample W, which is located on the outer peripheryside of the projection. For example, the portion protruding(overhanging) beyond the outer periphery of the projection is greatlyaffected by heat from plasma.

The surface of such outer edge of the sample W has a temperaturedistribution in which the temperature is higher than at the inside andrapidly increases from the inside toward the outside. Thus, in etchingthe sample W, in order to process such outer edge with the samedimensions as the central surface, it is effective to locally increasethe concentration of reaction products and adherents above and on theouter periphery of the sample W. According to the above configuration ofthis variation, the second mixed gas with a high composition of productsand adherents is introduced from the position near the outer edge of thesample W with good uniformity in the circumferential direction of theouter periphery of the sample W. Thus the within-wafer andcircumferential uniformity of processing of the sample W can beenhanced.

Second Embodiment

A second embodiment of the invention is described with reference to FIG.8, which is a vertical cross-sectional view schematically showing theconfiguration of the main part of a processing unit according to thesecond embodiment of the invention. The same elements as those in theembodiment of FIGS. 1 to 5 may be referred to by their referencenumerals, but are not described in detail. In this embodiment, incontrast to the first embodiment, the inner periphery side of the gasdiffusion ring is not covered with a ring cover.

In the vacuum vessel of this embodiment, as in the first embodiment, agas diffusion ring 204 is mounted above the sidewall upper end of avacuum vessel wall member 205, and a ring-shaped vacuum vessel wallmember 801 constituting the vacuum vessel is located above the gasdiffusion ring 204. The gas diffusion ring 204 is sandwiched and heldbetween the ring-shaped vacuum vessel wall member 801 and the sidewallupper portion of the lower vacuum vessel wall member 205.

In the gas diffusion ring 204 of this embodiment, its outer peripheralwall is exposed to ambient air outside the vacuum vessel and constitutesthe vacuum vessel outer wall. The inner peripheral wall of the gasdiffusion ring 204 is exposed inside the processing chamber 217 andfaces the plasma. A second mixed gas, which is supplied from a gassupply pipe 304 coupled to the outer wall of the gas diffusion ring 204,is introduced into the processing chamber 217 through a gas introductionhole 302 located in the inner peripheral wall. Thus, in this embodiment,a first mixed gas is introduced toward the sample W from a gas diffusionplate 206 located at the upside of the processing chamber 217 andopposed to the sample W, and the second mixed gas is introduced inwardfrom the inner wall upper portion of the processing chamber 217 abovethe sample W.

The gas introduction hole 302 of this embodiment is composed of slitslocated at a generally equal height in the circumferential direction ofthe ring from the lower end of the inner sidewall of the gas diffusionring 204. This configuration of the gas introduction hole 302 composedof the slits enhances the uniformity of the second mixed gas, whichextends at the upper portion of the inner wall of the processing chamber217 above the sample W and supplied from the periphery of the spaceabove the sample W. This configuration can use the configuration shownin FIG. 5B, where the mating surface of vertically combined members onthe inner periphery side has projections and recesses, which form slitswhen the upper member is connected to the lower member.

More specifically, the slits serving as the gas introduction hole 302are composed of a plurality of continual or adjacent portions in thecircumferential direction of the ring and arranged generallycircumferentially. The width of the slit in the height direction isconfigured so that the second mixed gas from the gas supply pipe 304fills the inner gas channel 301 at a high pressure enough to reducenonuniformity in the flow rate of the second mixed gas flowing into thelow-pressure processing chamber 217 through the slits locatedcircumferentially.

Thus the second mixed gas is introduced uniformly from the inner wall ofthe cylindrical processing chamber 217 above the sample W toward theinside. Hence the density of gas and products or the distribution ofplasma above the sample W can be affected to enhance the radial andcircumferential uniformity of processing on the sample W. For example,the first mixed gas of a first composition being rich in materials withhigh etching reactivity is introduced from the gas diffusion plate 206located above and opposed to the sample W, and the second mixed gas of asecond composition being rich in gas components generating adherents isintroduced from the outer periphery side of the sample W. Thus theconcentration of products in the processing chamber 217 on the outerperiphery side of the sample W has a reduced nonuniformity in the radialdirection of the sample W, and the nonuniformity of processing on thesample W is reduced.

Third Variation

Another variation of the above embodiment is described with reference toFIG. 9. As in the foregoing, the same elements as those alreadydescribed may be referred to by their reference numerals, but are notdescribed in detail.

FIG. 9 is a vertical cross-sectional view schematically illustrating theconfiguration of the main part of a processing unit according to anothervariation of the embodiment shown in FIG. 1. In contrast to the aboveembodiment, the processing unit of this variation does not include,above the vacuum vessel, a radio wave source that supplies an electricfield for generating a plasma in the processing chamber inside theprocessing unit. Furthermore, the processing gas supplied into theprocessing chamber is supplied toward the central axis of the processingchamber from a gap arranged in a ring shape on the outer periphery sideof the ceiling of the processing chamber.

In the processing unit according to this variation, a plasma isgenerated in the processing chamber 217 by an electric field between asample stage 208 and an upper electrode 901. The sample stage 208 islocated in the processing chamber 217 and includes an electrode to whichelectric power is supplied from a high-frequency power supply 911. Theupper electrode 901 constitutes an upper lid of the vacuum vessel, islocated above and opposed to the sample stage 208, and is coupled toground potential. As in the embodiment shown in FIG. 2, the electrode inthe sample stage 208 is coupled to a high-frequency bias power supply213 and supplied with high-frequency power for producing a biaspotential on the surface of the sample W.

The vacuum vessel of this variation includes a vacuum vessel wall member905 constituting the sidewall and the bottom, an upper electrode 901placed thereabove and constituting a lid member, and a gas diffusionring 204 placed on the outer periphery side thereof and hermeticallyheld therebetween for maintaining the pressure difference between theinside of the processing chamber 217 and the outside of the vacuumvessel. The upper electrode 901 is mounted above the sidewall upper endof the vacuum vessel wall member 905 via a gap. At this upper end, aflange 905′ extends toward the central axis of the generally cylindricalvacuum vessel or processing chamber 217. The upper electrode 901, thevacuum vessel wall member 905, and the gas diffusion ring 204 sandwichedtherebetween are coupled to ground potential to avoid abnormal dischargedue to potential difference among them.

The gas diffusion ring 204 placed on the outer periphery side of theupper electrode 901 is supplied with a mixed gas via an opening-closingvalve 916. The mixed gas is obtained by combining a plurality of (two)gas flows, where the flow rate of each gas is adjusted by a flow rateregulator 910 a, 910 b. The supplied mixed gas fills the inner gaschannel 301 and flows through a gas introduction hole 302 located in theinner peripheral wall into a gap 903 between the gas diffusion ring 204and the sidewall of the upper electrode 901 which is placed inside andopposed thereto. Then the mixed gas diffuses through the underlying gap903 communicating below therewith between the upper electrode 901 andthe flange 905′, and flows into the processing chamber 217 along thelower surface of the upper electrode 901, which is the ceiling of theprocessing chamber 217.

The gap 903 is located circumferentially at the upside of the processingchamber 217 above the sample W because the flange 905′ extendscircumferentially at the upper end of the cylindrical vacuum vessel wallmember 905. The width of the gap 903 is made generally uniform to reducecircumferential nonuniformity in the flow rate of the influent mixedgas.

Fourth Variation

Another variation of the embodiment of FIG. 1 is described withreference to FIGS. 10 and 11. FIG. 10 is a vertical cross-sectional viewschematically showing the configuration of the main part of a processingunit according to another variation of the embodiment shown in FIG. 1.FIG. 11 is an enlarged vertical cross-sectional view showing theconfiguration in the vicinity of the gas diffusion ring of theprocessing unit according to the variation shown in FIG. 10.

In the variation shown in FIG. 10, the processing unit comprises avacuum vessel including therein a processing chamber 217, and an exhaustapparatus placed below the vacuum vessel. An upper electrode 1101 isplaced at the upside of the vacuum vessel and hermetically held betweenthe inside and the outside of the vacuum vessel. The upper electrode1101 is supplied with high-frequency power from a high-frequency powersupply 1111, and supplies an electric field for plasma generation to theunderlying processing chamber 217.

A gas diffusion plate 1106 is placed below the upper electrode, facesthe processing chamber 217, and is exposed to plasma. The gas diffusionplate 1106 has through holes 1107, through which a first mixed gas isintroduced. The gas diffusion plate 1106, which may be made ofsemiconductor such as silicon having high purity, is composed of amaterial acting as a conductor for high-frequency power. The gasdiffusion plate 1106 constitutes the ceiling of the processing chamber217 and covers a range equal to or wider than the diameter of the sampleW. The gas diffusion plate 1106 faces the plasma generated in the spacebetween the sample stage 208 and the gas diffusion plate 1106.

A gas supply pipe 1108 is coupled to the upper electrode 1101 shapedlike a flat plate. As in the embodiment of FIG. 1, the first mixed gasis supplied to a gas diffusion space 1109 between the upper electrode1101 and the gas diffusion plate 1106. The gas diffusion space 1109extends in a range equal to or wider than the region where the throughholes 1107 are formed in the underlying gas diffusion plate 1106. A gasdistribution plate 1104 made of conductor is placed in the gas diffusionspace 1109. The gas distribution plate 1104 has a plurality of throughholes. The first mixed gas introduced into the gas diffusion space 1109passes through these through holes, diffuses in the gas diffusion space1109, and reaches the underlying gas diffusion plate 1106. In the gasdiffusion space 1109, the gap between the gas diffusion plate 1104 andthe overlying upper electrode 1101, and the gap between the gasdiffusion plate 1104 and the underlying gas diffusion plate 1106 areconfigured in size to avoid abnormal discharge.

A dielectric ring 1115 made of quartz or other material is placed on theouter periphery side of the upper electrode 1101. The dielectric ring1115 insulates the upper electrode 1101 from an upper ring 1102 placedtherearound and grounded. Below the upper ring 1102, a gas diffusionring 204 is placed between the upper ring 1102 and the sidewall of thevacuum vessel wall member 205.

As in the embodiment of FIG. 1, the gas diffusion ring 204 is suppliedwith a second mixed gas from a gas supply pipe 304. The second mixed gasis diffused from the inner peripheral side face of the gas diffusionring 204 and introduced into the processing chamber 217. A sample stage208 for mounting a sample W is placed in the processing chamber 217.High-frequency power is supplied from a high-frequency power supply 213to the electrode inside the sample stage 208, and produces a biaspotential on the surface of the sample W.

Furthermore, in this variation, inside the upper end of the outerperiphery of the generally cylindrical processing chamber 217, a ringcover 1103 made of dielectric and shaped like a flat plate constitutesthe ceiling of the processing chamber 217. The ring cover 1103hermetically covers the lower face of the dielectric ring 1115 on theprocessing chamber 217 side and the lower face (the face on theprocessing chamber side) of the outer periphery of the gas diffusionplate 1106. The ring cover 1103 is vertically divided into two members,and the second mixed gas is introduced through a gap formed from thesemembers into the processing chamber.

The sample W is processed as in the embodiment of FIG. 1. Morespecifically, from the through holes 1107 of the gas diffusion plate1106 opposed to the sample mounting surface of the sample stage 208, thefirst mixed gas of a first composition is introduced into the underlyingprocessing chamber 217. Simultaneously, from the inner wall of theprocessing chamber 217 on the upper outer periphery side above thesample W, the second mixed gas of a second composition is introducedtoward the center of the processing chamber 217.

An electric field from the upper electrode 1101 excites the suppliedfirst and second mixed gas into a plasma, by which the sample W isetched. Reaction products associated with the processing and particlesin the plasma migrate downward through the space of the processingchamber 217 on the outer periphery side of the sample stage 208, and areejected from an opening located at the bottom of the vacuum vessel,which serves as the inlet of a vacuum pump 209. The processing chamber217, the sample stage 208, and the vacuum pump inlet are arrangedconcentrically. The plasma, gas, and products in the processing chamber217 have axisymmetrical distribution with respect to this center. Thuscircumferential nonuniformity in the processing of the sample W isreduced with respect to the center of the sample W.

In this variation, a solenoid coil 1112 for supplying a magnetic fieldfor plasma generation to the space of the processing chamber 217 abovethe sample W is placed on the outer periphery of the vacuum vessel.However, the plasma may be generated solely by an electric field.

As shown in FIG. 11, the gas diffusion ring 204 is placed above theupper end of the vacuum vessel wall member 205. Furthermore, the upperring 1102 is placed above the gas diffusion ring 204. These arehermetically attached so as to maintain the gas pressure differencebetween the inside and the outside of the vacuum vessel. The upperelectrode 1101 shaped like a flat plate and constituting the lid of thevacuum vessel, the underlying gas diffusion plate 1106, and thedielectric ring 1115 are coupled to each other and moved up above thevacuum vessel wall member 205 together with the underlying ring cover1103 when the processing unit is opened to atmosphere for maintenanceand inspection.

At the upper end of the processing chamber 217 on the outer peripheryside, the ring cover 1103 made of quartz or other dielectric covers thelower face of the dielectric ring 1115 on the processing chamber 217side and the inner wall of the sidewall upper end of the grounded vacuumvessel wall member 205 on the processing chamber 217 side. In thisvariation, the ring cover 1103 is a vertical combination of a pluralityof (two) members. The upper ring cover 1103′ is coupled to thedielectric ring 1115, and the lower ring cover 1103″ is engaged with theinner wall of the vacuum vessel wall member 205.

The gas diffusion ring 204 is placed on the outer periphery side of thering cover 1103 and above the upper end of the vacuum vessel wall member205. As in the first embodiment, the gas diffusion ring 204 constitutesthe vacuum vessel and is exposed outside the vacuum vessel as its outerwall. The inner peripheral wall is opposed to the outer peripheral wallof the upper ring cover 1103′ across a gap 1105′. The second mixed gasfilling the gas channel 301 therein flows into the gap 1105′ from thegas introduction hole 302 located in the inner peripheral wall.

The influent second mixed gas migrates downward in the gap 1105′ andflows through a gap 1105 communicating therewith between the upper ringcover 1103′ and the lower ring cover 1103″ toward the center of thegenerally cylindrical processing chamber 217. Then the second mixed gasflows into the processing chamber 217 from an opening 1105″ of the gap1105 facing the processing chamber 217. The gap 1105 is located at theupside of the inner wall of the processing chamber 217 above the sampleW and generally circumferentially on the outer periphery side of thesample W. The height of the gap 1105 is approximately uniform. Thus theinflow rate of the second mixed gas has a reduced nonuniformity in thecircumferential direction of the sample W. Furthermore, the height ofthe gap 1105 is larger than the diameter or height of the gasintroduction hole 302, thereby facilitating diffusion of the secondmixed gas in this gap.

Thus the second mixed gas filling the gas channel 301 in the gasdiffusion ring 204 flows inward into the gap 1105 through the gasintroduction hole 302 composed of a plurality of through holes or atleast one slit communicating with the gas channel 301. The second mixedgas turns around and diffuses in the gap 1105, and is introduceduniformly into the processing chamber from the opening 1105″ of the gap1105 facing the processing chamber 217. Such introduction of theprocessing gas increases radial or circumferential uniformity in thedensity distribution of products or other particles and plasma. Thus theuniformity of processing is enhanced.

Third Embodiment

A third embodiment of the invention is described with reference to FIG.12, which is a vertical cross-sectional view schematically showing theconfiguration of the main part of a processing unit according to thethird embodiment of the invention. As in the foregoing, the sameelements as those already described maybe referred to by their referencenumerals, but are not described in detail.

FIG. 12 primarily shows the vacuum vessel of the processing unit. Theprocessing unit of this embodiment includes a vacuum vessel, aninduction coil 1205 placed thereabove, and a vacuum pump 209, which isan exhaust apparatus placed below the vacuum vessel.

In contrast to the first and second embodiment, the means for supplyingan electric field for plasma generation into the processing chamber 217in the vacuum vessel according to this embodiment is the induction coil1205 placed above a dielectric lid member 1201, which constitutes thevacuum vessel above the processing chamber 217. More specifically, inthis embodiment, the induction coil 1205 is supplied with high-frequencypower from a high-frequency power supply 1211. As a result, an electricfield is induced in the space above the sample stage 208 in theprocessing chamber 217, and the processing gas introduced into theprocessing chamber 217 is excited into a plasma.

In the vacuum vessel in this embodiment, a lid member 1201 constitutinga disc-shaped lid of the vacuum vessel is placed above the sidewall ofthe grounded, generally cylindrical vacuum vessel wall member 205. Thelid member 1201 is made of dielectric so that an induced electric fieldcan be introduced into the processing chamber 217 from the inductioncoil 1205, which is placed with a gap above the lid member 201concentrically or helically with respect to the cylinder. The lid member1201 is hermetically connected with the vacuum vessel wall member 205 tomaintain the gas pressure difference between the inside and the outsideof the processing chamber 217.

As in the embodiment shown in FIG. 1, the generally cylindricalprocessing chamber 217, the sample stage 208, and the opening at thebottom of the vacuum vessel wall member 205 serving as the inlet of thevacuum pump 209 are arranged concentrically. Furthermore, in thisembodiment, the induction coil 1205 is also arranged outside the vacuumvessel concentrically with respect to the central axis of the samplestage 208 on the outer periphery side thereof.

Although not shown, a metal plate made of conductor is placed betweenthe induction coil 1205 and the lid member 1201 so as to cover the uppersurface of the lid member 1201, and functions as a so-called Faradayshield. This metal plate is radially provided with a plurality ofslit-shaped notches across the windings of the induction coil 1205. Theslit-shaped notches introduce the induced electric field into theprocessing chamber 217, and prevent interaction of the inner wall of thelid member 1201 with the induction coil 1205 due to capacitive couplingin the processing chamber 217.

At the center of the lid member 1201, a gas supply unit 1204 forsupplying the processing gas into the processing chamber 217 is fit intothe lid member 1201. More specifically, the gas supply unit 1204 isplaced inside a hole at the center of the lid member 1201, and facesdownward the inside of the processing chamber 217 and upward the outsidethereof. The gas supply unit 1204 has at its center a gas introductionhole 1207 for introducing a first mixed gas into the processing chamber217. Furthermore, a gap 1203 having a uniform size is located betweenthe gas supply unit 1204 and the lid member 1201 generallycircumferentially around the gas introduction hole 1207. A second mixedgas is introduced into the processing chamber 217 through the gap 1203.

The gas introduction hole 1207 is a through hole extending from theupper surface of the dielectric gas supply unit 1204 exposed outside thevacuum vessel to the lower surface opposed to the sample mountingsurface of the sample stage 208 and exposed to plasma. The upper end ofthe gas introduction hole 1207 is coupled to a gas supply pipe forsupplying the first mixed gas. The slit-shaped gap 1203 located on theouter periphery side of the gas introduction hole 1207 communicates witha ring-shaped gas channel 1206 coupled to a gas supply pipe of thesecond mixed gas and located in the upper portion inside the gas supplyunit 1204. The second mixed gas passes through the gap 1203 and isintroduced into the processing chamber 217 from above the sample W.

The outer peripheral wall of the gas supply unit 1204 having anaxisymmetrical shape with respect to the center coaxial with the gasintroduction hole 1207 is separated by the gap 1203 from the lid member1201 into which the gas supply unit 1204 is fit. As shown, the gap 1203has a divergent shape radiating outward from the central axis as it goesdownward. That is, gap 1203 is shaped like an inverted funnel. Thus thesecond mixed gas filling the overlying ring-shaped space diffusesthrough the gap 1203 and flows out of the ring-shaped opening facing theprocessing chamber 217 toward the outer periphery side of the sample Wor the processing chamber 217.

According to such configuration of this embodiment, the first mixed gasof a first composition is introduced into the processing chamber 217toward the center of the sample W, and the second mixed gas of a secondcomposition is introduced toward the outer periphery side of the sampleW. Hence the density of gas and products or the distribution of plasmaon the upper surface of the sample W and in the space thereabove insidethe processing chamber 217 can be affected to enhance the radial andcircumferential uniformity of processing on the sample W.

The gas supply unit 1204 may be vertically divided into a plurality ofmembers. The lower member may be inserted into the center hole from thelower side of the lid member 1201 constituting the inner wall of theprocessing chamber 217, the upper member may be attached from the upperside of the lid member 1201, and these members may be connected tointegrally constitute a gas supply unit 1204. As in the secondembodiment, the size of the gap 1203 in this embodiment is configured tobe approximately uniform in the circumferential direction so that thegap 1203 is filled with the second mixed gas supplied to the ring-shapedgas channel 1206 to reduce circumferential nonuniformity in thediffusion of gas passing through the gap 1203.

1. A plasma processing apparatus for processing a wafer mounted on asample stage placed in a vacuum processing chamber using a plasmagenerated in the vacuum processing chamber, the plasma processingapparatus comprising: a plate disposed in the vacuum processing chamberabove and opposed to the wafer, the plate having a through hole throughwhich a first processing gas is introduced; a generally band shaped gapdisposed in the vacuum processing chamber; and a gas channel which isdisposed circumferentially outside of the vacuum processing chamber andcommunicated with the gap, wherein a second processing gas is suppliedinside the gas channel, at least one hole or slit disposed between thegas channel and the gap for communicating the gas channel with the gap,wherein the gas channel is disposed inside of a ring-shaped membercommunicated with the gap through the at least one hole or slit providedin an inner peripheral wall of the ring-shaped member wherein a firstportion of the gap is defined between the inner peripheral wall of thering-shaped member and a first cylindrical portion of an outerperipheral surface of a ring cover facing and spaced from the innerperipheral wall of the ring-shaped member, and a second portion of thegap is defined between an inner surface of a wall of the vacuumprocessing chamber and a second portion of the outer peripheral surfaceof the ring cover facing and spaced from the inner surface of a wall ofthe vacuum processing chamber wherein a height of the gap is configuredto be larger than a height or diameter of the hole or slit, and thewafer is processed while the first processing gas and the secondprocessing gas having different compositions are supplied into thevacuum processing chamber.
 2. The plasma processing apparatus accordingto claim 1, wherein the ring cover and the vacuum processing chamber arearranged vertically and adjacently.
 3. The plasma processing apparatusaccording to claim 1, wherein the ring cover and the inner surface of awall of the vacuum processing chamber face the plasma.
 4. The plasmaprocessing apparatus according to claim 1, wherein the gap is formedwith a predetermined slope.
 5. The plasma processing apparatus accordingto claim 1, wherein the sample stage includes temperature control meansfor the wafer, and the outer periphery of the wafer is located outsidethe wafer mounting surface of the sample stage.
 6. The plasma processingapparatus according to claim 1, wherein the gap communicates with thevacuum processing chamber through an opening provided between an end ofthe second portion of the ring cover and the inner surface of a wall ofthe vacuum processing chamber.
 7. The plasma processing apparatusaccording to claim 6, wherein the second portion of the outer peripheralsurface of the ring cover and the portion of the inner surface of a wallof the vacuum processing chamber facing and spaced from the secondportion of the outer peripheral surface of the ring cover are taperedsuch that the second portion of the gap is directed inwardly towards anouter peripheral edge of the sample stage.